How can bone names be copied across an axis?
make Sure you are in Edit Mode!

Step One: Create just ONE side of the armature and name the bones.

Step Two: Select Bones Wanted to copy to across an axis.

Step Three: Set 3D Cursor to origin by hitting Shift-S: 'Cursor to Selected' (Make sure origin is in center of armature).
Step Four: Press Shift+D and click the mouse button

Step Five: Hit Cntrl+M and then hit X (Or y if you are using the y-axis)

Step Six: Click the mouse button and hit w and select 'Flip Names'

Profit!